Semiconductor device fabrication requires that a semiconductor wafer pass through a number of manufacturing stages. For example, masking, patterning, etching, and film deposition may be performed numerous times in order to manufacture the multiple layers and features of a semiconductor device. The need to track individual wafers through the manufacturing process has given rise to the use of a trackable wafer scribe, typically in the form of a numerical designation readable by both human operators and machines.
Scribing a semiconductor at the beginning of the manufacturing process allows the wafer to be tracked through the remainder of the processing steps. Several problems arise, however with scribing a wafer at the beginning of the manufacturing process. For example, particles and contaminants can collect in the scribed area during a deposition step, then spread to other areas of the wafer during subsequent processing steps. The result is often the formation of unwanted short-circuits, open circuits, and other defects in the completed devices. A common approach to solving these problems is the use of a scribe on the backside of the wafer only, rather than the front side. In fact, it is common for manufacturers of larger semiconductor wafers, e.g. 300 mm, to place scribes exclusively on the backside, rather than on the front as used with 200 mm wafers.
The use of a backside wafer scribe avoids many of the problems associated with the presence of a front side scribe during some manufacturing steps, particularly those performed in the early stages of wafer fabrication, however the utility of backside scribes is limited. One of the primary limitations of the use of backside wafer scribes is that some steps in the wafer fabrication process can operate to eliminate or obscure the scribe. Backside scribes are particularly susceptible to damage or eradication during steps near the end of the wafer fabrication process. For example, following steps for passivation and bond pad formation, further steps are typically performed in preparation for eventual die separation and packaging, including backgrind, resulting in the removal of the scribe. An additional problem encountered is that some testing and packaging equipment is designed for use with wafers having a front side scribe, and upgrading such equipment to read backside scribes can be quite costly.
Due to these and other problems, the application of a front side scribe as late in the wafer fabrication process as possible, but prior to process steps which may interfere with the use of the backside scribe, would be desirable in the arts. Such a front side scribe would permit continuity in tracking wafers until die separation. However, conventional scribing methods are not amenable to scribing the front side of a wafer in the advanced stages of the fabrication process. This is due to the characteristics and materials present on the wafer as it nears completion. For example, the films present on the wafer front side may include dielectrics, metals, and etch-stop materials. As a result, the wafer surface may have inherent variability in thickness and composition, which may be particularly extreme at the edges of the wafer outside of the boundaries of the saleable devices. This variability extends not only to the surface of the individual wafer, but also to variations from wafer to wafer and from lot to lot. This is particularly true at the wafer edge where the front side scribe is commonly applied. The use of typical laser scribing equipment on such surfaces often results in variations in depth, profile and ultimately in readability of the scribe and may also cause contamination of the wafer surface.
Improved front side semiconductor wafer scribes and scribing methods would be useful and advantageous in the arts. Such scribes and methods would provide increased readability for front side scribes useful for wafer tracking during processing while mitigating contamination and reducing cost.